Switch with mercury wetted contacts



June 1965 SHINI'CHI TONOOKA EFAL 3,199,993

- SWITCH WITH WHITE.) CQRTILGTS Filed Dec 4, 1962 F ig United States Patent signors to Leeds and Northrop Company, Philadelphia,

Pa., a corporation of Pennsylvania Filed Dec. 4, 1962, Ser. No. 242,150 20 Claims. (Cl."200152) This'invention relates to a tap switch of the type hav-' ing mercury wetted contacts and has for an object the provision of an improved mercury wetted contact switchof low resistance and particularly suited for rapid automatic operation in low level precision direct current apparatus.

In prior lift-turn-drop type mercury switches, a large contact surface of mercury must be broken in a small angular travel. A substantial force is required to break such a large contact surface of mercury. This force is in addition to the force required in the lift mechanism itself. The lift-turn-drop mechanism also has a tendency to splash mercury if the rotary contact is dropped rapidly. In the present invention a rotary sliding type of motion is employed. This motion is imparted to a bridging con-tact member which in combination with an automatic mercury feeding system distributes mercury to all of the switch contact areas and recirculates the mercury through a common mercury reservoir. The sliding motion ofthe bridging contact minimizes the torque required for switch operation by gradually reducing the surface area of mercury separated in moving the bridging contact from one bridged contact to another. The area of mercury separated is so small that the force due to surface tension on final contact separation is negligible. During rotation of the bridging contact, the mercury also acts as a lubricant and as a result the power required for motion is small and the switch lends itself to reasonably sized power operators which can be automatically and rapidly actuated. The switch may also be operated manually, intermittently, over a wide range of speeds, and exposed to the atmosphere while maintaining consistently low contact resistance.

In accordance with one aspect of the present invention, there is provided a tap switch with mercury wetted contacts including a reservoir for mercury. A common contact is supported in the reservoir and a plurality of separate contacts are arranged along the common contact and electrically insulated therefrom. Structure is provided in the reservoir and supported adjacent the common contact to provide a narrow passage for supplying mercury by capillary action from the reservoir to the contiguous switch contact surfaces. A slidable contact means bridges the common contact and at least one of the separate contacts, the slidable contact means being adapted upon movement thereof through its path of travel to deliver mercury retained on the face of the contact to the contact surface of the separate contact as it engages the same. Thus the bridge contact acts as a mercury transfer contact. More particularly, movement of the slidable contact serves to pump mercury from the top of the narrow passage .and introduce the mercury between adjacent contact surfaces to wet the adjacentsurfaces of the contacts with mercury.

For further objects and advantages thereof and for a more detailed understanding of the invention, reference is to be had to the following description taken in conjunc-' tion with the accompanying drawings in which:

FIG. 1 is a vertical section of a rotary switch embodying the present invention; and

FIG. 2 is a sectional plan view taken along the line 2-2 of 'FIG. 1.

Referring to FIGS. 1 and 2, it will be seen that the rotary switch 10 is mounted on a base 111 of electrical insulating material. is adapted to receive mercury 13 is positioned on the base 11. The reservoir 12 is made from suitable material such, for example, as copper. Disposed centrally oftherreservoir.r12is a circular projection 15 around.

which is positioneda. circular contact or collector ring 16. The: collector ring 16 is positioned with its upper surface in the same plane as the upper surface of projection 15, this plane being referred to as the contact plane. Ring-lfiissupported on spaced bushings 16a,-

FIG. 2, thuspermitting the mercury 13- to pass beneath the ring 16 upwardly through a narrow annular passageway 17 formed between the inner circumference of the ring 16 and. the outer circumference of projection 15.

Three studs 16b extend through the bushings 16a and anchor the ring 16in place with nuts 18 drawn tightly against the base plate 111. The studs 16b provide for electrical connection to the common contact 16. It will be appreciated that the showing of the width of passageway 17 in FIGS. 1 and2 is exaggerated for purposes of clarity and that the passageway 17 in actual practice is in the nature of an annular capillary. Extending in circular array about the axis of the collector ring 16 are a plurality of separate contacts illustrated in the form of contact poles 19, only two of which are shown in FIG. 1. The contact poles 19 are supported by insulating members 20 carried by the reservoir 12. The insulating members 20 extend through openings in the bottom of reservoir 12 and insulate the contact poles 1-9 from the reservoir 12. The contact poles .19 are provided at their upper ends with hat contact surfaces19a which are in the same contact plane as the upper surface of collector ring .16. The lower ends of the contact poles 19 are in the form of threaded studs 1% which extend through the insulating base '11. Each of the studs "1% is provided with a nut 22 which secures the poles 19 in their respective positions Within 1% provide for electrical connection to the respective poles 19.

As may be seen in FIG. 1, the mercury 13 passes upwardly from the bottom of the reservoir 12 through the annular passage 17 until it reaches the contact plane. A bridging contact in the form of a contact disc 24 is carried by an insulating pin 25, preferably nylon or equivalent, mounted in the end of an arm 26 which is carried by the lower end of a shaft 27 extending through a cover 28; The arm 26 is fixed to the end of the shaft 27 as by a set screw 29, FIG. 1. The shaft 27 is adapted to be actuated-from any suitable source either automatically or manually. The collector ring 16, the contact poles 19 and the contact disc 24 are all made of metal, preferably copper and all surfaces along the contact plane, the walls of the annular opening 17 and the floor of the reservoir 12, are amalgamated so that mercury will wet the surfaces.

The contact disc 24 is driven by the pin 25 which has. a running fit within a hole 24a, FIG. 2, located in the center of the disc 24. The contact disc 24 rests 'on the contact surface 19a of a contact pole 19 and the contact surface of collector ring 16, the disc 24 being free to rotate about its oWn center on the bear-ing surface provided by pin 25. As previously mentioned, mercury travels from the reservoir 12 up the vertical annular opening 17 by capillary action. Since the collector ring 16 is adjacent to the supply of mercury along its inner periphery at .17, the contact surface of the collector ring will be wetted with mercury and be lubricated thereby due to transfer of mercury through surface tension. Additionally, the disc 24 in moving across the annular opening 17 and the sur- A cup-shaped reservoir 12 which.

face of ring 16 is wetted with mercury. Mercury is carried by the contact disc 24 to the contact surfaces 19a of the contact poles 19. If a contact pole 19 has insufficient mercury on its surface, there will be greater friction and hence resistance to the sliding motion at that part of the disc 24 over the corresponding contact portion 19a. As a result, motion of the driving pin 25 in moving the contact disc 24 to the next pole 19 will cause the disc 24 to rotate about its own center. This rotation of the contact disc 24 will thereby transfer mercury along the amalgamated portions of the disc from the collector ring 16 and the annular opening 17 to the corresponding contact pole 19 at a rate depending upon the depletion of mercury n the surface 19a of the pole. Thus, as long as the disc 24 is wetted with mercury, all switch contact surfaces 19a of the poles 19 will be automatically wetted with mercury to maintain a low and constant contact resistance.

The mercury which has filled the annular passage 17 by capillary action is moved by a pumping action induced by motion of the contact disc 24. This pumping action will depend on the speed of motion of the contact disc 24 which controls the rate of removal of mercury from annular passage 17. Any excess mercury on the contact surfaces will fall into the common reservoir 12 and become recirculated on operation of the switch 10. The motion of the contact disc 24 over the poles 19 and collector ring also tends to have a self cleaning action on their surfaces.- Most of the foreign particles and oxide impurities which are formed on these surfaces when the switch is exposed to the atmosphere are wiped off into the reservoir where they float and remain on the surface of the mercury pool. As the excess mercury drops from the contact plane into the reservoir, most of the foreign matter in the droplets is confined to the reservoir surface and a cleaner mercury solution is recirculated upwardly from the bottom of the well through the annular passage 17 From the foregoing description, it will be seen that the slide type of actuation of the bridging contact disc 24 lends itself to a relatively simple mechanism and eliminates the need of a shaft bearing in the contact areas.

This construction permits a smaller switch configuration for a given contact surface area and in addition eliminates the danger of mercury leakage through shaft bearrngs.

While the switch 10 has been illustrated as of the multipole shorting type where the contact disc 24 during rotation thereof engages an adjacent pole before breaking contact with the previous pole, it is to be understood that the invention is applicable to rotary switches where poles 19 are spaced between inactive poles so that the diameter of disc 24 is not adequate to concurrently engage two of the active contact poles.

While as pointed out above the contact 24 may be moved automatically or manually, it is preferablethat the contact be operated periodically at frequent intervals to prevent accumulation of oxide or other foreign material on the contacts. a

While a preferred form of the invention has been described and illustrated, it is to be understood that further modifications thereof may be made within the scope of the appended claims.

What is claimed is: t p I 1. A tap switch with mercury wetted contacts comprising a plurality of contacts spaced one from the other, mercury transfer contact means for closing a circuit between a selected one of said contacts and at least one of the remaining contacts, means for supporting said pluralityof contacts and said transfer contact means for relative movement one to the other through a path which brings said transfer contactmeans to a selected circuit-closing position between said selected one contact and others of said remaining contacts, a reservoir for mercury disposed adjacent said plurality of contacts and adjacent said trans fer contact means, capillary means within said reservoir extending to said path of relative movement for transferring mercury from said reservoir to said transfer contact means and thence to said plurality of contacts by said relative movement between said transfer contact means and saidplurality of contacts.

2. A tap switch according to claim 1 in which bearing structure is provided for said mercury transfer contact means for rotation thereof as said supporting means moves said contact means from one to another of said circuitclosing positions.

3. A tap switch according to claim 1 in which said capillary means comprises a narrow capillary passage formed between one of said contacts and a projection supported closely adjacent to said last-named one of said contacts.

4. A tap switch according to claim 2 in which bearing structure is provided for said mercury transfer contact means for rotation thereof as said supporting means moves said contact means from one to another of said circuit closing positions.

5. A tap switch with mercury wetted contacts comprising a reservoir for mercury, a plurality of stationary contacts supported within said reservoir and electrically insulated from said reservoir and one from the other, a stationary common contact supported within said reservoir adjacent said plurality of stationary contacts, means in said reservoir adjacent said common contact forming a narrow passage for capillary transfer of mercury from saidreservoir to the region of said common contact, mercury transfer contact means bridging at least one of said stationary contacts, at least a portion of said common contact, and at least a portion of said narrow passage, for conveying mercury from said narrow passage to and along the contact surfaces of said stationary and said common contacts.

6. A tap switch according to claim 5 in which said mercury transfer contact means is a circular contact, and further including means for supporting said circular contact for rotation about an axis thereof.

7. A tap switch according to claim 5 in whichsaid stationary contacts, said common contacts, and said narrow passage are disposed in circular array.

8. A tap switch according to claim 5 wherein the contact surfaces of said stationary contacts and said common contact are disposed in a common contact plane above the normal level of mercury in said reservoir and wherein the upper extremity of said narrow passage terminates in said common contact plane.

9. A tap switch according to claim 5 wherein said means in said reservoir adajacent said common contact forming a narrow passage includes a projection supported in said reservoir adjacent said common contact for forming said narrow passage.

10. A tap switch according to claim 9 wherein said mercury transfer contact means is a circular contact, and further including means for supporting said circular contact for rotation about an axis thereof.

11. A tap switch with mercury wetted contacts comprising a reservoir for mercury, aplurality of stationary contacts supported within saidvreservoir and extending upwardly above the normal level of mercury in said reservoir and in spaced relation one with the other, the

upper surfaces of said stationary contacts forming a common contact plane, a stationary common contact supported by said reservoir and of length coextensive with said plurality of said stationary contacts in their spacedapart relationship and having its upper surface terminating at said contact plane, said plurality of contacts and said common contact being electrically insulated one from the other, means including structure in said reservoir supported adjacent said common contact and forming a narrow passage therebetween for capillary transfer of mercury upwardly from said reservoir to said-contact plane, and bridging contact means having a contact surface of sufiicient length and breadth to overlap said narrow passage, a portion of said common contact means and at least one of said plurality of stationary contacts, said surface of said bridging contact means being disposed in the region of said contact plane for conveying mercury from said narrow passage to and along the opposing contact surfaces.

12. A tap switch according to claim 11 wherein said common contact is a circular contact comprised of a ring structure.

13. A tap switch according to claim 12 wherein said means including structure in said reservoir is supported coaxially within said ring structure and said narrow passage is an annular passage formed therebetween.

14. A tap switch according to claim 13 wherein said ring structure is supported within said reservoir with passageways extending beneath said ring structure for communication between said reservoir and the bottom of said annular passage for flow of mercury therethrough.

15. A tap switch according to claim 11 wherein said bridging contact means comprises a contact disc having a diameter sufiicient to span said common contact and the far side of one of said separate contacts and said narrow passage, and means for supporting said contact disc for rotation about the axis thereof.

16. A tap switch according to claim 15 wherein said common contact, said stationary contacts and said narrow passage are disposed in circular array including a rotatable actuator shaft disposed coaxially of said circular array, an arm carried by said shaft for rotation therewith, with the outer end of said arm supporting a pin for driving said contact disc.

17. A tap switch with mercury wetted contacts comprising a reservoir for mercury, a circular contact supported in said reservoir, a plurality of separate contacts arranged around the central axis of said circular contact and electrically insulated therefrom, a projection supported in said reservoir adjacent said circular contact to provide an annular passage for a supply of mercury from said reservoir, and rotatable contact means bridging said circular contact, said annular passage, and at least one of said separate contacts, said rotatable contact means being adapted upon rotation thereof to pump mercury from the top of said annular passage and between the adjacent contact surfacesof said rotatable contact, at least one of said separate contacts, and said circular contact to wet said adjacent surfaces of said contacts with mercury.

18. A tap switch with mercury wetted contact surfaces comprising a reservoir for mercury, a circular contact supported within said reservoir and having a contact surface disposed in a contact plane above the normal level of mercury in said reservoir, a plurality of contacts supported within said reservoir and disposed concentric of said circular contact in spaced relation one from the other, each of said plurality of contacts having a contact surface disposed in said contact plane, a circular projec tion supported within said reservoir and disposed concentric of said circular contact forming therebetween a narrow annular capillary passage for transfer of mercury from said reservoir to said contact plane, a mercury transfer contact having a circular contact surface disposed in said contact plane with said circular contact surface having a diameter suificient to simultaneously overlap a portion of said circular contact, a portion of said capillary passage, and at least one of said plurality of contacts, and means supporting said! mercury transfer contact for both rotation about the axis of said circular contact surface and rotation about the axis of said circular contact whereupon mercury will be transferred from said capillary passage to the contact surface of said mercury transfer contact and thence to the contact surfaces of said circular contact and said plurality of contacts.

19. A tap switch according to claim 18 in which said plurality of contacts are insulated one from the other and from said reservoir.

20. A tap switch according to claim 19 in which said means supporting said mercury transfer contact includes a rotatable actuator shaft disposed above and concentric of said circular contact, a lever arm carried by said actuator shaft for rotation therewith, and a crank pin mounted on the outer end of said lever arm connected in driving relationship to said mercury transfer contact for rotation relative thereto.

References Cited by the Examiner UNITED STATES PATENTS 2,856,486 10/58 ONeill 200-152X 3,008,023 11/61 Hayner 200152 ROBERT K. SCHAEFER, Acting Primary Examiner. 

1. A TAP SWITCH WITH MERCURY WETTED CONTACTS COMPRISING A PLURALITY OF CONTACTS SPACED ONE FROM THE OTHER, MERCURY TRANSFER CONTACT MEANS FOR CLOSING A CIRCUIT BETWEEN A SELECTED ONE OF SAID CONTACTS AND AT LEAST ONE OF THE REMAINING CONTACTS, MEANS FOR SUPPORTING SAID PLURALITY OF CONTACTS AND SAID TRANSFER CONTACT MEANS FOR RELATIVE MOVEMENT ONE TO THE OTHER THROUGH A PATH WHICH BRINGS SAID TRANSFER CONTACT MEANS TO A SELECTED CIRCUIT-CLOSING POSITION BETWEEN SAID SELECTED ONE CONTACT AND OTHERS OF SAID REMAINING CONTACTS, A RESERVOIR FOR MERCURY DISPOSED ADJACENT SAID PLURALITY OF CONTACTS AND ADJACENT SAID TRANSFER CONTACT MEANS, CAPILLARY MEANS WITHIN SAID RESERVOIR EXTENDING TO SAID PATH OR RELATIVE MOVEMENT FOR TRANSFERRING MERCURY FROM SAID RESERVOIR TO SAID TRANSFER CONTACT MEANS AND THENCE TO SAID PLURALITY OF CONTACTS BY SAID RELATIVE MOVEMENT BETWEEN SAID TRANSFER CONTACT MEANS AND SAID PLURALITY OF CONTACTS. 